Generally, steam turbines used in power generation facilities such as thermal power plants and nuclear power plants are provided with a steam governing valve apparatus on an upstream side of the steam turbine for controlling the steam flow rate according to load changes and for cutting off the supply of steam in response to an emergency. The steam governing valve apparatus that is arranged upstream of the high-pressure turbine is disposed in series with a main stop valve.
FIG. 14 is an explanatory drawing that illustrates a conventional steam governing valve apparatus that is used in a steam turbine. In FIG. 14, a main stop valve 110 that instantly stops steam from flowing into the steam turbine in response to an emergency or the like with respect to the steam turbine, and a steam governing valve 120 for controlling a steam flow rate are shown. A side portion of a valve main body 121 of the steam governing valve 120 communicates with and is connected to the main stop valve 110. The steam governing valve apparatus has a top cover 122 on an upper end portion of the valve main body 121. A valve seat 123 that forms a raised shape is provided in an inner portion of the valve main body 121, and a valve rod 125 that is coupled to a valve element 124 that butts against the valve seat 123 penetrates through the top cover 122 and is connected to an oil cylinder 127.
A steam flow from an unshown boiler or the like flows into the main stop valve 110 as indicated by an arrow I, and flows out from the steam governing valve 120 as indicated by an arrow O. When hydraulic pressure acts on the oil cylinder 127 of the steam governing valve 120, the valve element 124 moves vertically via the valve rod 125, and the steam governing valve 120 performs opening/closing operations. The steam flow rate is controlled by the opening/closing operations, and steam flows into an unshown steam turbine. Note that, a piston 126 and a closing spring 129 are fitted into the oil cylinder 127 of the steam governing valve 120, and an oil supply and discharge port 128 is arranged underneath the piston 126. A hydraulic device such as a servo valve or a dump valve is connected to the oil supply and discharge port 128, although an illustration thereof is omitted from FIG. 14.
Meanwhile, the main stop valve 110 is configured similarly to the steam governing valve 120, and has a top cover 112 on an upper end portion of the valve main body 111. A valve seat 114 forming a raised shape is provided in an internal portion of a valve main body 111, and a valve element 115 that butts against the valve seat 114 is connected to an oil cylinder 117 through a valve rod 116. When hydraulic pressure acts on the oil cylinder 117, the valve element 115 moves vertically via the valve rod 116, and the main stop valve 110 performs opening/closing operations. Supply of steam and cutting off of the supply of steam are executed by way of the opening/closing operations. Note that, reference numeral 113 in FIG. 14 denotes a strainer.
Generally, in a steam governing valve apparatus that is used in a steam turbine of a power generation facility, in particular in the steam governing valve 120, unsuitable cases such as the occurrence of noise, vibrations, erosion and material deterioration are known. The steam governing valve 120 is configured so as to control the steam flow rate by way of a throttling function between the valve element 124 and the valve seat 123, that is achieved by moving the valve element 124 in the valve chest that comprises the valve element 124 and the valve seat 123. It is considered that the aforementioned noise or vibrations arise because the noise or vibrations are induced by turbulence in the flow of steam around the valve element 124 or an unstable flow or the like (for example, see Patent Document 1).
Recently, accompanying increases in steam conditions at power generation facilities (supercritical pressure plants) and increases in the single unit capacity of steam turbines, improved technology that incorporates further enhancements is being proposed (for example, see Patent Documents 2 and 3).
As shown in FIG. 15 and FIG. 16, a steam governing valve 120 in the aforementioned Patent Documents 1 and 2 comprises a valve element 124 that is formed with a spherical curved surface and has a recessed portion 130 comprising an edge 131 at a rim, and a valve seat 123 that has a spherical curved surface so as to gradually expand towards a downstream side from a position that the valve element 124 contacts, and is configured so that the spherical curved surfaces of the valve element 124 and the valve seat 123 contact each other. Accordingly, in the steam governing valve 120, on a bottom portion side of the valve element 124, because the recessed portion 130 having the edge 131 at the rim is provided, from in a range from a minute opening degree to the vicinity of an intermediate opening degree as shown in FIG. 17(A), a flow of steam along the valve element 124 is separated at the edge 131 of the valve element 124 and becomes a stable flow along the valve seat 123, and thus the generation of noise or vibrations can be prevented.
Further, in a steam governing valve described in Patent Document 3, a flow guide is provided inside a recessed portion of a valve element, and the flow guide is mounted on the valve main body side.